1. Field
The invention is in the field of detection of lines on the surface of a road or highway from a moving motor vehicle.
2. State of the Art
According to the Intelligent Transportation Systems of America newly developed strategic ten year plan, vehicle safety systems such as a road line detector could save thousands of lives on our nations highways. The staggering increase in cell phone use by drivers and introduction of high-tech in-vehicle entertainment and navigation systems has resulted in increased driver distraction. As a result, research and development of Lane Departure and Warning Systems has increased and mandating such devices in Federal vehicles for evaluation are being considered.
It has been realized since at least 1973, U.S. Pat. No. 3,708,668, that it would be desirable to have a device for motor vehicles that would detect road lines and sound or display an alarm to alert the driver of the vehicle when the vehicle approached or crossed such a line so the driver could correct and stay within his or her lane and avoid unintentional lateral drift or lane departure.
Since the present invention can detect vehicle lateral drift, drunk-driving characteristics such as excessive weaving can also be detected.
It was recognized as early as U.S. Pat. No. 3,708,668 that a significant problem with such a system is compensating for different ambient light levels. Thus, such a system has to be able to detect road lines in bright sunlight as well as in darkness at night. U.S. Pat. No. 3,708,668 provides a pair of sensors that balance each other when both detect a road surface, but result in a warning signal when one sensor detects a light reflecting line and the other does not. U.S. Pat. No. 4,143,264 provides a bridge circuit with an impedance element controlled by an integrated output of the bridge circuit to maintain a balance of the bridge for ambient light conditions and vary sensitivity of the detector with light conditions. Various infrared, laser, and CCD camera devices have also been suggested, U.S. Pat. Nos. 4,348,652, 5,979,581, 5,790,403, and 5,957,983. U.S. Pat. No. 5,982,278 shows various arrangements of detectors for detecting road lines and special line arrangements but does not teach any specific detection circuitry. The search for a practical device to provide satisfactory road line detection has continued and a number of devices have been suggested.
U.S. Pat. No. 5,318,143 provides a device that utilize infrared emitters and detectors beneath a vehicle that could be used to detect a stripe placed in the middle of a lane. Sunlight and shadows, however, can be observed on the roadway under the vehicle around the time the sun is setting, due to the extreme angle of the sun. This extraneous sunlight would likely interfere with the detector operation resulting in severely degraded performance. Further, road lines are located along the sides of the lane and never in the middle of the lane therefore, the device is impractical. However, the need remains for a reliable and inexpensive line detector that can be easily mounted in side mirrors or other practical location on a vehicle and effectively detect road lines under various ambient lighting conditions.
In my co-pending application Ser. No. 09/865,070, I disclose a system which determines if lines are detected within successive fixed periods of time in which it is expected that a line should be detected, and if a line is not detected in such periods of time, indicating possible lateral drift of the vehicle out of the lane, an alarm is given. In such system, it has been found that extraneous signals, such as short noise signals or signals from road irregularities or items on the road can be mistaken for road line signals and keep the alarm from providing an alarm signal. Improvements can be made to such system to increase its accuracy of detection.
According to the invention, a detector for detecting light reflected from discontinuous lane dividing lines or other lines on a highway surface from a moving motor vehicle to determine the position of the vehicle on the highway includes a detector to detect light reflected from the surface of the highway and means to determine from the reflected light sensed not only the presence of road lines but a characteristic of the road line determined to be present to determine if the characteristic of the road line detected is consistent with previously detected road lines and therefore appears to be a valid road line. The alarm, when enabled, is activated unless a road line consistent with previously sensed road lines is sensed within successive fixed periods of time in which it is expected that a line should be sensed. The presently preferred system detects the beginning and end of a road line sensed and determines the length of the road line from the time between sensing of the beginning and end of the line. If the length is consistent with previously sensed road lines, the sensed road line is treated as a valid road line. If the length is not consistent, the sensed road line is not a valid line and may represent a noise signal or the sensing of something on the highway surface other than a valid line such as a paint spot, road kill or other debris on the road surface, a road reflector, etc. In such case, the inconsistent line sensed is ignored. Also, by using a programmed computer to evaluate the sensed line, various characteristics of the sensed line can be determined, and, in addition to determining whether the line sensed is a valid line, various other things, such as the type of line likely sensed or the speed of travel of the vehicle can be determined.
In addition, a line detector system must be able to accommodate daytime as well as nighttime driving for it to be a useful lane departure and warning system. The inventor has discovered that the use of large area photodiodes in conjunction with infrared emitters, energized while driving at night, allows the device to operate under all environmental lighting conditions. Large area photodiodes are used in such applications as remote control receivers in stereos and televisions. A large area photodiode has a large chip surface area that produces more photocurrent than small area photodiodes, therefore large area photodiodes are more sensitive to light and light level changes. Large area photodiodes are also more sensitive in very low light level conditions such as during nighttime driving. In the preferred embodiment, the large area photodiode produces a reverse voltage across the anode and cathode junction that increases or decreases proportionally with the infrared light striking the exposed silicon chip. The proposed Infrared Road Line Detector differs from prior art because it detects the time interval between the start and end of individual road line segments. This method provides superior timing parameters for implementing capabilities such as vehicle speed calculations in addition to allowing faster validation that road line segments are detected. Finally, the waveform produced by light level changes associated with the start and end of a road line are very compatible with threshold detectors. Hence, the present patent offers a simple, inexpensive, versatile and very effective method to detect road lines under all lighting conditions, and in particular, at night. Detectors and emitters can be implemented on both sides of the vehicle in order to detect road lines on both sides of the lane resulting in a more functional invention. An analog to digital converter and microprocessor is added to the invention to allow sampling and analysis of solid road lines as well as individual road line segments.